Jars are used in the oilfield industry to deliver jarring blows to a tubing string in order to free a stuck section of pipe. Jars are also used in fishing operations, in order to free any object stuck in a downhole well. Double-acting jars are jars that are capable of delivering an upjar or a downjar to a tubing string. U.S. Pat. No. 5,906,239, describes a double-acting jarring tool that affords a user the option of delivering successive upjars, or successive downjars, and is complex.